1. Field of the Invention
The present invention relates to a false twister which nips yarn between crossed belts and imparts twist and feed to the yarn. Particularly, the invention is concerned with a false twister capable of controlling an untwisting tension of yarn in a simple construction to improve the yarn quality and is concerned with a controlling method of a false twister.
2. Prior Art
The construction of a drawing and false-twisting machine (draw texturizing machine) using this type of false twisters will now be described with reference to FIG. 5. The drawing and false-twisting machine is constituted by false twist units 1 which are arranged in a large number (210 spindles) side,by side in the direction perpendicular to the paper surface. Each false twist unit 1 has a first feed roller 3 for drawing out yarn (filament yarn) Y from a feed package 2 supported by a creel stand 2a. The yarn Y from the first feed roller 3 passes a primary heater and a ballooning plate 5 successively in this order, then is false-twisted by means of a false twister (nip twister) 6. The yarn Y thus false twisted passes a second feed roller 7, a secondary heater 8 and a third feed roller 9 successively in this sequence and is taken up as a take-up package 10 by means of a winder 10a. As a result, bulkiness is given to the yarn Y.
The false twister 6 is provided with a pair of crossed belts 11 and 12 to nip, twist and feed the yarn Y therebetween. Twists formed by the false twister 6 are propagated up to the first feed roller 3 and heat-set by the primary heater 4. That is, the upstream side of the false twister 6 is a twisting side and the downstream side thereof is an untwisting side.
In such false twister, the tension on the untwisting side exerts an important influence on the quality or physical properties (expansion and contraction, dyeability, etc.) of yarn, so various proposals have been made for controlling the contact pressure of belts so as to maintain the untwisting tension at a certain constant value.
In the conventional false twister, however, the construction for controlling the contact pressure of belts is complicated, thus resulting in increase of cost.